From: acase@Glue.umd.edu (Andrew Case)
Newsgroups: sci.space.tech
Subject: Re: Cole Process Asteroids as Space Habitats?
Date: 21 Dec 2000 17:11:13 -0500

Ian Stirling  <Inquisitor@I.am> wrote:
>
>Even a very simplistic analysis that I posted a while back, based on the
>surface tension of iron, and using that to work out the resonant frequency
>of the bubble seems to indicate that a meter is hard, 100m nearly impossible.
>Another problem is there is no force centering the bubble in the shell.
>
>However, if you can extrude sheets or coils of metal into space, then there
>are many interesting shapes you could make, some of which would suit
>habitation.

For the amount of energy needed to run the Cole process, it would be
possible to enclose the entire asteroid in a thin balloon inflated
with carbon monoxide. Heat the whole thing (balloon, asteroid and
CO) to the appropriate temperature and let iron/nickel/etc plate
onto the inner surface of the balloon until you have the desired
wall thickness. The appropriate temperature would be dictated by
the need to have a mixture of carbon monoxide and metal carbonyls
in (near-)equilibrium with the metals on the asteroid and balloon. The
timescales might be long, though. The balloon needs to be at a higher
temperature than the asteroid in order to favor the deposition of metal
on the balloon, but that ought not be too hard (at least relative to
heating up the entire asteroid to its melting point). One possibility
is to spot heat using a laser, or once you have a little metal deposited
you could induction heat spots to encourage deposition where it does
the most good. Of course solar heating of the whole balloon is possible,
but perhaps undesireable since that makes maintaining the temperature
differential hard. Best bet is probably solar spot heating of the balloon.

When it's all over you have an asteroid inside a pressure vessel,
so you can work on the asteroid in your shirtsleeves if you so
desire (ignoring the fact that the dust would choke you...). The
pressure vessel would be some weird nickel/iron steel
with trace amounts of PGMs etc, but that need not be a big deal.
More problematic is the likelihood of releasing huge amounts of
volatiles as the asteroid heats up. These would have to be dealt
with in order to avoid popping the balloon, or poisoning the
carbonyl reaction (I'm not a chemist so I don't know if that's likely
to be an issue). Since one of the reasons for goind to the asteroid
in the first place might well be to harvest volatiles, a plant for
capturing and condensing them as they boil off could be quite a
plus.

Now if we can just find funding... :)
More problematic is finding the right asteroid. With thousands of
NEAs out there it's quite likely that only a very few are worth
trying to exploit commercially.

.....Andrew
--
Andrew Case				|
acase@plasma.umd.edu			|
Institute for Plasma Research		|
University of Maryland, College Park	|

From: acase@Glue.umd.edu (Andrew Case)
Newsgroups: sci.space.tech
Subject: Re: Cole Process Asteroids as Space Habitats?
Date: 23 Dec 2000 14:54:44 -0500

In article <3A4304C3.B2E83EB8@ASmit.edu>,
>Wow.  I hadn't heard about metal carbonyl chemical vapor deposition, so
>I looked it up.  This is a fabulous idea.  I do have a bunch of
>questions, though:
>0.  Can you supply a reference discussing CO plating of iron and nickel?

The mark of a true geek: numbering from zero. (it's a compliment :)
anyway, I haven't found really good references (been busy writing
my dissertation), but you can get a rough idea of one application from
http://ginsburg.ipm.virginia.edu/research/PM/Exp/infiltration.htm

>1.  One website I looked at said plating is expensive because it's
>slow.  How long would it take to plate, say, a meter-thick layer?

No idea. Undoubtedly the limiting factors are the flow rate of the
carbonyl and the surface temperature of the substrate (and possibly
the kinetics of the decomposition process, but I assume that it goes
faster the hotter the surface is).

>2.  At what temperature does this process occur?  Even roughly?  How
>does that temperature compare with the melting/vaporization temperature
>of the plastic you propose to make the balloon out of?

100 Celsius for Nickel, a bit less for Iron, and quite a bit higher (IIRC)
for platinum.

>3.  At what pressure does this process occur?  What is the largest
>sphere which could be constructed from plastic sheeting without bursting
>under the pressure?  Are there many asteroids of this size?

CVD on earth is done at a variety of pressures. I know for certain that
it is done at atmospheric pressure, and I'm pretty sure that Plasma-
Assisted CVD is done at below atmospheric pressure (at least some times).

>4.  Does the process occur efficiently in the presence of significant
>impurities?  (i.e., rocks, and vapors released by heated rocks)  You
>mentioned the vapor issue in your post; it's worth doing some research
>to investigate.

Give me the funding and I will give you the answer :)
More seriously - I'm trying to find out the answers to these questions
myself. Once I have a bit more time I'll put in a few days in the
library and see what I can come up with. I'll post a summary when
I get a chance.

>Re the need to keep the envelope hotter than the interior: the thermal
>inertia of the asteroid might help you here.

Exactly my thought: I think ensuring that there is adequate circulation
might be a problem, since you can't rely on convection. You'd probably
need fans to keep things moving, which raises problems with dust (again).

.....Andrew

--
Andrew Case				|
acase@plasma.umd.edu			|
Institute for Plasma Research		|
University of Maryland, College Park	|